98 XJ 4.0 ECU replacement question(s) - JeepForum.com
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post #1 of 4 Old 01-10-2020, 12:13 AM Thread Starter
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1998 FSJ Cherokee 
Join Date: Feb 2010
Location: Western Australia
Posts: 5
Question 98 XJ 4.0 ECU replacement question(s)

I have a 98 XJ with a small (okay large) problem...he stalls when driving on warmer days. He always starts up again either right away or after a short cool-down, but it's dangerous to be driving down the road and have him quit. And I'd like to get the problem resolved before my husband lights him on fire.

Here's a rundown of the situation:
Never happens in winter
No codes, no "check engine" no "no bus" etc...(all codes previously addressed)
Have replaced everything recommended (everything)
He's in great running condition since so much work has been done trying to fix this problem...idles well, drives fine until it doesn't.

My question is about the ECU...someone recently mentioned that they'd heard of cracks forming in older Jeep "computer boards", and when they heat up, the crack expands and then circuity-wirey things can break.

Sounds legit to me... just wanted an opinion(s) on replacing the ECU. I can exchange mine for a refurbished one for a reasonable price (the seller claims to "reprogram the refurbished ECU with the information from my existing ECU.") And I've been told new ECU's are not available for an XJ of this age, is that also true?

Any info or opinions greatly appreciated. If this sounds ridiculous you can tell me that, too.

Thanks from Tasmania...

agkennedy is offline  
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post #2 of 4 Old 01-10-2020, 04:38 AM
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2000 XJ Cherokee 
Join Date: Apr 2002
Location: out in the garage - Minneapolis
Posts: 27,943
If you have addressed all the more common and logical causes for unexplained stalling, then yes on very rare occasions the ECU can fail. No new ECU's are available. On-Line refurbished ECU sellers have less the perfect customer service and sometimes have quality control issues. If you locate a donor Cherokee with the same engine/transmission and the ECU part numbers match, you can install that ECU with no reprogramming, except if the donor Cherokee has the optional factory installed SKIM anti-theft system activated.

Thermal failures that lead to stalling are most often a faulty Crankshaft Position Sensor.

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post #3 of 4 Old 01-10-2020, 08:53 AM
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jtec's Avatar
2014 JK Wrangler 
Join Date: Oct 2017
Posts: 7,630
My thoughts-

I hate really hate, replacing PCM's, just a quirk IDK.

You said "Have replaced everything recommended (everything)"
spend a moment and tell us WHAT you changed .
You are or have used a scanner to check codes? explain about getting codes.

A SWAG stalls and will restart - has me thinking
CKP and or CKP CMP wiring.
Fuel cavitation,

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #4 of 4 Old 01-15-2020, 12:50 AM Thread Starter
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1998 FSJ Cherokee 
Join Date: Feb 2010
Location: Western Australia
Posts: 5
Thanks for the replies...

What is SWAG?

There was one code awhile back that had to do with temperature, and it was addressed at the time. There are currently no codes (according to mechanic).
Entire fuel line has been checked/fuel pump replaced/tank cleaned while in there, etc...
MAP sensor replaced
TPS replaced
Camshaft position sensor replaced when distributor assembly was replaced
Crankshaft position sensor replaced
Relays checked (traded AC/fuel pump/ASD relays around)
New coolant temp sensor
Ignition components checked (coil replaced)
Spark plugs inspected
Wiring harness inspected

I will have a look at the wiring to some of the sensors. It is strictly heat related, meaning I can drive all winter with no issues and then summer comes and it the issue appears again. Since it's summer here, it's time for some more troubleshooting.

Thanks again for the info.

agkennedy is offline  

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